During my recent reading, I came across a fascinating mention of the fleet pennant board. This method, used in squadron/fleet settings, allowed the flagship to signal an individual ship with remarkable precision, a testament to the meticulousness of historical naval communication.
Each vessel of the Georgian Royal Navy had its own "number," which was listed in the Navy List of the time, e.g., 703 | Victory | 100. This is how ships were identified with each other.
Many of us are familiar with the phrase 'Make our number' from period shows and books. This signal hoist included the Union flag and the ship's navy list number. The authenticity of this process was confirmed by checking the number against the navy list and the private signal of the day, immersing us in the world of historical naval communication.
The pennant board is a shorthand way of distinguishing ships for which signals were intended when acting as part of a squadron. Each ship in the squadron would be assigned a two-pennant code and where it would be flown and hoisted when the flagship wished to address that ship singly.
The period signal books I've been able to handle have an incredible array of pennants somewhere (generally at the back) and have an interesting way of updating the ship names when needed.
I hope on my next visit to the National Maritime Museum in Greenwich to request to see some more of these "private" signal books.